Hydropneumatic shock absorber

ABSTRACT

The cylinder of a shock absorber is spacedly enveloped by a coaxial, axially substantially coextensive cylindrical outer shell. A piston in the cylinder carries a piston rod which passes in sealing engagement through an annular first axial end wall of the cylinder and the shell. The cylinder cavity and the annular chamber between shell and cylinder are connected near the second imperforate axial end wall of the shock absorber which is below the annular wall in the normal operating position. A resilient sleeve in the chamber seals the cylinder to the first end wall and serves as a check valve on bore, in the cylinder for radially outward flow of gas. A compressed gas cushion occupies the upper portion of the chamber. The remainder of the chamber, the cylinder cavity, and axial throttling passages in the piston are filled with liquid. Gas reaching the cylinder cavity is quickly returned to the chamber through the check valve during operation of the shock absorber.

a United States Patent 1 May 9, 1972 Wossner i541 HYDROPNEUMATIC SHOCKABSORBER [72] lnventor: Felix Wossner, Schweinfurt am Main, Germany [73]Assignee: Flchtel & Sachs AG, Schweinfurt am Main, Germany [22] Filed:Mar. 10, 1970 [21] Appl. No.: 18,229

[30] Foreign Application Priority Data Mar. 13, 1969 Germany ..P l9 12781.2

[52] U.S. Cl. ..188/3l5, 188/269, 188/322 [51] Int. Cl. ..F16f 9/06,F16f9/34, F16f9/40 [58] FleldoiSearch ..188/269.315,322

[56] References Cited UNITED STATES PATENTS 3,520,384 7/1970 Nicholls..188/26 2,155,978 4/1939 Oberstadt.. ...,l88/269 2,214,038 9/1940Beecher ....188/315 3,339,680 9/1967 Tuneblom ..l88/322 FOREIGN PATENTSOR APPLICATIONS 1,077,606 5/1954 France 1 88/3 15 7 PrimaryExaminer-George E. A. Halvosa Attorney-Kelman and Berman ABSTRACT Thecylinder of a shock absorber is spacedly enveloped by a coaxial, axiallysubstantially coextensive cylindrical outer shell. A piston in thecylinder carries a piston rod which passes in sealing engagement throughan annular first axial end wall ofthe cylinder and the shell. Thecylinder cavity and the annular chamber between shell and cylinder areconnected near the second imperforate axial end wall of the shockabsorber which is below the annular wall in the normal operating posi- 8Claims, 3 Drawing Figures HYDROPNEUMATIC SHOCK ABSORBER This inventionrelates to shock absorbers, and particularly to an improvement inhydropneumatic shock absorbers.

In its more specific aspects, the invention is concerned with shockabsorbers of the type having an outer shell and an inner cylinderelongated in a common direction, the cylinder having a longitudinal axisand being received in the shell so as to define a chamber therewith. Thechamber and the cylinder cavity are axially bounded by a first annularend wall and a second imperforate end wall. A piston axially slidable inthe cavity divides the same into two compartments and is formed withthrottling passages connecting the compartments. A piston rod attachedto the piston extends through one compartment and outward of thecylinder cavity through the annular end wall. The cavity and chamber arefluid-filled, and the piston rod is sealed to the first end wall whichis normally above the second end wall.

Known shock absorbers of the afore-described type are equipped withvalves near the second end wall which permit liquid flow between thecavity and the chamber as needed when the piston rod moves into and outof the cylinder. The chamber is partly filled with air and communicateswith the atmosphere. The valves are relatively complex, therefore costlyand a source of malfunction. Moreover, they occupy a significant axialportion of the shock absorber which is not otherwise useful, and therebyrequire a generally undesirable overall lengthening ofthe device.

In another known shock abosrber, the gas in the chamber has a highpressure, and an annular floating piston separates the gas from the oil.The floating piston must be sealed to the shell and to the innercylinder in sliding engagement, and the engaging walls must be finishedwith great precision at relatively high cost to ensure a reasonableservice life of the piston.

It is a primary object of the instant invention to provide ahydropneumatic shock absorber having the desirable operatingcharacteristics of the known devices described above, but being simplerin its design and capable of being manufactured at lower cost.

The shock absorber of the invention is normally installed with itsannular end wall and exposed piston rod above the cylinder and itsimperforate end wall. In this position, a gas cushion under a pressuremuch greater than atmospheric pressure is almost completely confined inthe chamber between the cylinder and the outer shell. Liquid almostcompletely fills the compartments of the cylinder cavity above and belowthe piston, and fills the remainder of the chamber in direct contactwith the gas cushion. The chamber and the compartment of the cylindercavity below the piston communicate permanently for flow of liquidtherebetween without significant throttling effect. The sealing memberwhich engages the piston rod for sealing it to the annular end wall ofthe cylinder is exposed to the liquid in the cavity.

Other features, additional objects, and many of the attendant advantagesof this invention will readily be appreciated as the same becomes betterunderstood from consideration of the following detailed description ofpreferred embodiments when considered in connection with the appendeddrawing in which:

FlG.l shows a hydropneumatic shock absorber of the invention inelevational section on its axis; and

H052 and 3 show the bottom portions of modified shock absorbers of theinvention in views corresponding to that of FlG.1.

Referring now to the drawing in detail, and initially to FlG.l, there isseen a hydropneumatic shock absorber having an elongated inner cylinder1 coaxially received in an outer, cylindrical shell 2 whose diameter isabout one third greater than that of the cylinder 1. A piston 3 isaxially slidably received in the cylinder cavity 6 and mounted on oneend of a piston rod 4 passing axially outward of the cylinder 1 throughan annular plug 5 which forms one axial end wall of the cylinder 1 andthe shell 2.

A heavy ring 7 is set into the lower end of the cylinder 1. Its annularbottom face 8 is spherically convex and conformingly engages acorrespondingly concave face of the imperforate integral bottom wall 9of the shell 2, thereby holding the cylinder centered in the shell 2.Circumferentially spaced notches 10 in the ring face 8 form radialapertures connecting the cylinder cavity 6 with an annular chamber 11between the cylinder 1 and the shell 2.

During normal shock absorber operation, the cavity 6 is entirely filledwith shock absorber oil or a like liquid which also occupies the lowerend of the chamber 11, but has been partly omitted from the drawing forthe sake of clarity. The greater upper portion of the chamber 11 isoccupied by a cushion 12 of air, nitrogen, or other suitable gas under apressure much higher than atmospheric pressure in direct contact withthe oil in the chamber 1 l.

The plug 5 is generally of stepped cylindrical shape. lts axially outeror top portion is wide enough to be received in the cylindrical shell 2with a tight sliding fit. The axially central portion has an outerdiameter equal to that of the slightly enlarged top end of thecylinder 1. The lowermost or axially innermost portion of the plug 5fits into the enlarged top end of the cylinder 1 and is received in thesame. A resilient sleeve 13 of oil-resistant synthetic rubber covers thecentral portion of the plug 5, the enlarged top end ofthe cylinder 1,and an axially adjacent part of the main portion of the cylinder 1 whichis of uniform diameter. The sleeve 13 thereby seals the plug 5 to thecylinder 1. Small radial bores 14 in the last-mentioned part of thecylinder 1 are normally covered and closed by the sleeve 13.

Because the compressed gas cushion 12 is in direct contact with theliquid in the chamber 11, and the chamber is permanently connected withthe cylinder cavity 6 through the wide apertures 10, small amounts ofgas may enter the cavity and form a temporary gas bubble 15 at thehighest point of the cylinder cavity adjacent the bores 14. When thepressure within the cylinder cavity exceeds that in the chamber 11, thegas lifts the sleeve 13 sufficiently from the orifices of the bores 14to permit its return to the chamber 11 whereas gas from the chambercannot enter the cylinder cavity, the sleeve 13 serving also as a checkvalve.

An annular baffle disc 16 is set into the cylinder cavity 6 in an axialposition below the lowest limit of the gas bubble 15 that is expectedduring operation of the shock absorber. The baffle 16 envelops thepiston rod 14 with a wide clearance so as not to interfere with axialfluid flow. It is axially aligned with the orifices of axial, valvedthrottling passages 17 provided in the piston 3 in a conventionalmanner. Jets of liquid discharged from the passages 17 during downwardmovement of the piston 3 impinge on the baffle 16 and are prevented fromintimately mixing with the gas in the bubble l5, and thereby fromforming a foam or froth which would reduce the effectiveness of theshock absorber.

Leakage of fluid from the cylinder cavity along the piston rod 14 isprevented by a sealing ring 18 recessed in the plug 5, but exposed tothe pressure fluid in the cylinder cavity.

A fluid-tight seal between the plug 5 and the shell 2 is formed by anO-ring 19 set into an annular groove 20 of the widest plug portion. Theupper wall of the groove is approximately conical so that the fluidpressure in the shock absorber wedges the O-ring between the shell 2 andthe plug 5.

A sheet metal ring 21 attached to the outer face of the shell 2 and aportion 22 of the vehicle frame, not otherwise shown; provide abutmentsfor an interposed helical compression spring 23 coaxial with the shockabsorber and conventional in itself. The threaded outer end 27 of thepiston rod 4 and a ring 28 fixedly fastened to the bottom wall 9 of theshell 2 provide attachments for the sprung and unsprung masses of thevehicle. A cap 29 holds the plug 5 in place.

The afore-described shock absorber operates as follows: When the staticor dynamic load on the shock absorber increases, the piston rod 4 movesinward of the cavity 6, and oil flows upward through the throttlingpassages 17, thereby 7 placed by the entering portion of the piston rod4 flows through the apertures 10 from the cavity 6 into the chamber 11against the resilient resistance of the gas cushion 12 which increasesas the cushion is being compressed. During inward movement of the pistonrod 4, the fluid pressure in the chamber 11 is higher than in the uppercompartment of the cavity 6 downwardly bounded by the piston 3, and thecheck valve at the sleeve 13 remains closed.

When the load on the shock absorber is reduced, and the piston rod 4moves axially outward of the cavity 6 at a speed partly determined bythe throttling effect of the passages 17. The gas cushion 12 expands anddrives oil into the cavity 6 to replace the volume of the piston rodportion withdrawn from the cylinder 1. As long as the piston rod 4 movesoutwardly of the cavity 6, the fluid pressure in the upper cylindercompartment is greater than in the chamber 11, and the accumulated gasbubble 15 can return to the chamber 11 through the bores 14 and theopened check valve of the sleeve 13. Not enough gas can accumulate inthe cavity 6 to reach below the baffle ring 16 where it may be exposedto turbulent liquid flow of sufficient energy to disperse the liquid ina foam.

FlGS.2 and 3 illustrate modified simple arrangements for holding thelower end of the cylinder 1 coaxially centered in the shell 2. As shownin FIG.2, the lower terminal portion 24 of the cylinder 1 is enlargedfor sliding fit in the shell 2. The frustoconically tapering flange partof the cylinder 1 which connects the enlarged cylindrical portion 24 tothe uniformly cylindrical main portion downwardly bounds the chamber 11and is formed with circumferentially distributed apertures which permitoil to flow between the cavity 6 and the chamber 11 without significantthrottling effect, the combined flow sections of the apertures 25 beingmuch greater than the effective flow sections of the passages 17 not allof which are opened simultaneously by their respective valves, as isknown in itself.

In the modified shock absorber partly seen in FlG.3, the lower end ofthe cylinder 1 is bent over outwardly twice at right angles so as toform a rimmed radial flange 26, the cylindrical rim engaging the innerwall of the shell 2, and the radial flange portion downwardly boundingthe chamber 11 and being formed with apertures 25, as described withreference to FIG.2.

The shock absorbers of the invention have been found to functionsmoothly and to have entirely satisfactory characteristics although theyare quickly assembled from few and simple components and can bemanufactured at relatively low cost. The only valves employed are thesimple, conventional flap valves on the throttling passages 17 in thepiston 3, and the check valve at the sleeve 13 for gas removal from thecavity 6 which additionally serves other functions. it is not necessaryto separate the liquid and gas in the shock absorber of the invention bya floating piston which is customary in similar conventional devices andis a source of shock absorber failure if its sealing rings are worn.

The shock absorbers of the invention are installed with the piston rod 4projecting upwardly from the shell 2 as is preferred in manyapplications, as with a spring 23 interposed between the vehicle frameand the outer shock absorber shell 2.

While a relatively large gas bubble 15 has been shown in FIG.1 for theclarity of pictorial representation, the amount of gas which canaccumulate at the top of the cavity 6 under all practical operatingconditions is so small that the sealing ring 18 is wetted with oil atall times, and the seal between the ring 18 and the piston rod 4 needonly be liquid-tight, not gastight. Leakage losses from the shockabsorber, if any, can be made up by forcing gas or oil under pressurefrom the outside past the O-ring 19.

In the absence of valves at the lower end of the cylinder 1, it is verysimple to keep the lower cylinder end coaxially centered in the shell 2,and the arrangements shown in the several Figures are merelyillustrative of convenient solutions to a problem which may be complexin conventional shock absorbers of the hydropneumatic type. The dishedbottom wall 9 of the shell 2 serves as a baffle which prevents liquidfrom entering the chamber 11 at a velocity sufficient to causedispersion of the compressed gas in the liquid.

lf further simplification of the shock absorber is desired, the valvebores 14 may be replaced by notches made in the upper rim of thecylinder 1 and normally covered by the sleeve 13. The plug 5 is modifiedaccordingly to provide passages from the notches to the topmost portionof the cavity 6.

Other modifications and variations will readily suggest themselves tothose skilled in the art on the basis of the above teachings, and itshould be understood therefore that the invention may be carried outotherwise than specifically disclosed without departing from the spiritand scope of the appended claims.

What is claimed is:

1. A hydropneumatic shock absorber comprising, in combination:

a. an outer shell member and an inner cylinder member elongated in acommon direction,

1. said cylinder member having a longitudinal axis and being received insaid shell member,

2. said members defining an therebetween;

b. a first annular end wall and a second imperforate end wall axiallybounding said chamber and a cavity in said cylinder member;

c. a piston member axially slidable in said cavity and axially dividingthe same into a first compartment adjacent said first end wall and asecond compartment adjacent said second end wall,

1. said piston member being formed with a throttling passage havingrespective orifices in said compartments for flow of fluid between saidcompartments;

d. a piston rod member attached to said piston member and extendingtherefrom through said first compartment and outward of said cavity;

e. sealing means sealing said piston rod member to said first end wall,

1. the first end wall being upwardly spaced from said second end wall inthe normal operating position of said shock absorber;

f. connecting means defining a permanently open connecting conduitbetween said chamber and said second compartment for flow of fluidtherebetween;

g. a gas under a pressure substantially greater than atmosphericpressure substantially confined in said chamber adjacent said first endwall in said operating position of the shock absorber;

h. a liquid substantially completely filling said compartments, saidpassage, and said conduit, and filling the remainder of said chamber indirect contact with said gas in said operating position of the shockabsorber;

i. check valve means connecting a portion of said first compartmentaxially adjacent said first end wall and radially remote from saidpiston rod with said chamber for permitting flow of fluid toward saidchamber only;

j. an annular baffle member arranged in said first compartment axiallyintermediate said check valve means and said piston member in axialalignment with an orifice of said throttling passage in said firstcompartment,

1. said cylinder member being formed with an opening connecting saidfirst compartment with said chamber and having an orifice in saidchamber adjacent said first end wall,

2. said check valve means including a resilient sleeve member on saidcylinder member and normally covering said orifice,

3. said first end wall having an axially terminal portion conforminglyreceived in an end portion of said cylinder member, and

4. said first end wall having another axial portion contiguous to saidterminal portion and projecting from said cylinder member in an axialdirection.

annular chamber 2. In a shock absorber as set forth in claim 1. saidbaffle member having a central opening receiving said piston rod memberwith sufficient clearance to permit unimpeded passage of fluid betweensaid baffle member and said piston rod member.

3. A shock absorber as set forth in claim 1, wherein the resistance ofsaid connecting means to flow of said liquid therethrough between saidchamber and said second compartment is much smaller than the resistanceof said piston member to axial flow between said compartments.

4. In a shock absorber as set forth in claim 1, locating meanssubstantially centering the terminal portion of said cylinder memberadjacent said second end wall in said shell member, whereby said cavityis annular about said axis.

5. In a shock absorber as set forth in claim 4, said locating meansincluding a ring member mounted on said cylinder member, said second endwall being of arcuate cross section and conformingly engaging said ringmember.

6. In a shock absorber as set forth in claim 4, said locating meansincluding a flange radially extending from said cylinder member andengaging said shell member.

7. In a shock absorber as set forth in claim 1, the cross section ofsaid other axial portion being substantially the same as the crosssection of the end portion of said cylinder member, said sleeve memberenveloping said other axial portion and said end portion for sealingsaid first end wall to the cylinder member.

8. In a shock absorber as set forth in claim 7, said cylinder memberhaving an axial part contiguously adjacent said end portion and formedwith said opening, said axial part being of smaller cross section thansaid end portion.

1. A hydropneumatic shock absorber comprising, in combination: a. anouter shell member and an inner cylinder member elongated in a commondirection,
 1. said cylinder member having a longitudinal axis and beingreceived in said shell member,
 2. said members defining an annularchamber therebetween; b. a first annular end wall and a secondimperforate end wall axially bounding said chamber and a cavity in saidcylinder member; c. a piston member axially slidable in said cavity andaxially dividing the same into a first compartment adjacent said firstend wall and a second compartment adjacent said second end wall,
 1. saidpiston member being formed with a throttling passage having respectiveorifices in said compartments for flow of fluid between saidcompartments; d. a piston rod member attached to said piston member andextending therefrom through said first compartment and outward of saidcavity; e. sealing means sealIng said piston rod member to said firstend wall,
 1. the first end wall being upwardly spaced from said secondend wall in the normal operating position of said shock absorber; f.connecting means defining a permanently open connecting conduit betweensaid chamber and said second compartment for flow of fluid therebetween;g. a gas under a pressure substantially greater than atmosphericpressure substantially confined in said chamber adjacent said first endwall in said operating position of the shock absorber; h. a liquidsubstantially completely filling said compartments, said passage, andsaid conduit, and filling the remainder of said chamber in directcontact with said gas in said operating position of the shock absorber;i. check valve means connecting a portion of said first compartmentaxially adjacent said first end wall and radially remote from saidpiston rod with said chamber for permitting flow of fluid toward saidchamber only; j. an annular baffle member arranged in said firstcompartment axially intermediate said check valve means and said pistonmember in axial alignment with an orifice of said throttling passage insaid first compartment,
 1. said cylinder member being formed with anopening connecting said first compartment with said chamber and havingan orifice in said chamber adjacent said first end wall,
 2. said checkvalve means including a resilient sleeve member on said cylinder memberand normally covering said orifice,
 3. said first end wall having anaxially terminal portion conformingly received in an end portion of saidcylinder member, and
 4. said first end wall having another axial portioncontiguous to said terminal portion and projecting from said cylindermember in an axial direction.
 2. said members defining an annularchamber therebetween; b. a first annular end wall and a secondimperforate end wall axially bounding said chamber and a cavity in saidcylinder member; c. a piston member axially slidable in said cavity andaxially dividing the same into a first compartment adjacent said firstend wall and a second compartment adjacent said second end wall,
 2. saidcheck valve means including a resilient sleeve member on said cylindermember and normally covering said orifice,
 2. In a shock absorber as setforth in claim 1, said baffle member having a central opening receivingsaid piston rod member with sufficient clearance to permit unimpededpassage of fluid between said baffle member and said piston rod member.3. A shock absorber as set forth in claim 1, wherein the resistance ofsaid connecting means to flow of said liquid therethrough between saidchamber and said second compartment is much smaller than the resistanceof said piston member to axial flow between said compartments.
 3. saidfirst end wall having an axially terminal portion conformingly receivedin an end portion of said cylinder member, and
 4. said first end wallhaving another axial portion contiguous to said terminal portion andprojecting from said cylinder member in an axial direction.
 4. In ashock absorber as set forth in claim 1, locating means substantiallycentering the terminal portion of said cylinder member adjacent saidsecond end wall in said shell member, whereby said cavity is annularabout said axis.
 5. In a shock absorber as set forth in claim 4, saidlocating means including a ring member mounted on said cylinder member,said second end wall being of arcuate cross section and conforminglyengaging said ring member.
 6. In a shock absorber as set forth in claim4, said locating means including a flange radially extending from saidcylinder member and engaging said shell member.
 7. In a shock absorberas set forth in claim 1, the cross section of said other axial portionbeing substantially the same as the cross section of the end portion ofsaid cylinder member, said sleeve member enveloping said other axialportion and said end portion for sealing said first end wall to thecylinder member.
 8. In a shock absorber as set forth in claim 7, saidcylinder member having an axial part contiguously adjacent said endportion and formed with said opening, said axial part being of smallercross section than said end portion.